The present invention relates to coilable tape rules, and more particularly, to such tape rules having an improved hook at the end thereof to reduce fatigue during repeated retraction of the tape into the casing.
Coilable metal tape rules are widely employed to facilitate measurement and return of the extended tape into the casing for storage and carrying purposes. Generally, the tapes are fabricated of metal and have an element secured to their outer end which is generally referred to as a hook so that the outer end of the tape rule may be engaged over (or against) a surface from which the measurement is to be taken. Generally the tape hook is a bent metal strip secured to the metal blade by rivets, although some tape hooks are far more complex in structure.
The spring motors utilized to retract the uncoiled tape into the casing are generally quite powerful, particularly with respect to longer tapes, and the speed of retraction is frequently substantial and subject to variation as the size of the coil increases. Because there is frequently an extended length of tape projecting from the case, and the aperture into the casing provides an effective pivot point, there is a tendency for the extended length of tape to flex or whip as it is being withdrawn into the casing. The mass of the tape hook is frequently such as to provide a second point of pivoting or flexure for the extended tape with the metal tape bending about the inner end of the hook. Moreover, if the lower surface of the tape adjacent the hook is not flush against the workpiece over which it is disposed, the pull exerted on the tape causes flexure about the end of the hook and may cause the end of the hook to mar the surface of the workpiece. As a result of this repeated flexing, there is a tendency for the metal of the tape to fatigue at the inner end of the hook.
Moreover, since the retraction of the blade into the casing is stopped rather abruptly by the abutment of the tape hook against the wall of the casing about the aperture, there is also a tendency for the shock loading about the rivets or other means for fastening the tape hook to the metal tape to produce fatigue in, and $hearing action on the metal tape. As a result, it is quite common for the metal tapes to fracture in the area of the tape hook and require replacement.
It is an object of the present invention to provide a coilable tape rule having a novel assembly of tape hook end coilable tape which reduces fatigue and shearing action on the metal tape.
It is also an object to provide such coilable tape rule in which the elements may be simply and readily fabricated and assembled.
Another object is to provide such a coilable metal rule in which the tape hook overlies the outer edge of the metal tape so as to substantially prevent the user from coming into contact with the relatively sharp corners at the outer edge and being injured thereby.